Specialists Tokyo climatological center JMA (Japan Meteorological Agency), conducted a preliminary study of the causes heavy rains that led to catastrophic flooding in Indochina.
Usually the summer monsoon, which brings rain to the region, lasts from May to October. In 2011, the rainy season lasted from June to September, but the rainfall was at 120-180% above the norm. That is, the intensity of the normal rainfall in some places could be exceeded 2-2.5 times! For four months in Chiang Mai (northern Thailand) fell 921 mm of precipitation (134% of normal) in Bangkok — 1251 (140%), Vientiane (Laos) — 1641 (144%), Phnom Penh — 835 mm (107%) . Heavy rains continued in the basin of the Chao Phraya and the first half of October.
Figure 1 Precipitation totals for the period from June to September, and their comparison with the norm in Chiang Mai, Bangkok and Phnom Penh Ventyane.
Figure 2 Excess monthly precipitation over the norm. The rate calculated for a number of years from 1981 to 2010
Climate scientists have found that the intensity of the convective processes in the four months from June to September in the band 10-20 ° N in South and Southeast Asia was very high, it is the cause of the unusual activity of the monsoon.
Figure 3 shows the average of four months (June-September, 2011) outgoing longwave radiation anomaly (V/m2). Over Indochina is a zone of negative anomalies, indicating the intense process of cloud and precipitation. (Data for granted NOAA).